The advent of a new round of stringent emissions legislation in Europe and North America is driving the implementation of new exhaust aftertreatment systems, particularly for compression-ignition (diesel) engines that exhibit high levels of soot and particulate matter in the engine exhaust. Exhaust aftertreatment technologies are currently in production that trap these particulate emissions. These diesel particulate filters (DPFs) require periodic regeneration to remove the built-up particulate matter (PM). The regeneration requires temperatures in excess of 540 C to efficiently oxidize the PM and clean out the filter. These temperatures are rarely achieved under normal operation in many diesel applications; therefore, an active regeneration approach is often required to guarantee periodic cleaning of the DPF.
Generally, the active regeneration is achieved by a post-injection of the main engine fuel injectors (injection of fuel during the exhaust stroke). The extra, uncombusted fuel enters the exhaust system where it oxidizes and thereby increases the exhaust gas temperature to the required levels for regeneration.
Improvements to this approach have been developed, notably, diesel dosing systems that inject hydrocarbons directly into the exhaust system.
There is a need to further improve a diesel dosing system to prevent excessive build-up of fluid pressure during hot shutdown.